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ABNORMALITIES OF FIXATION, SACCADE AND PURSUIT IN POSTERIOR CORTICAL ATROPHY
  1. Timothy Shakespeare1,
  2. Diego Kaski2,
  3. Keir Yong1,
  4. Ross Patterson1,
  5. Catherine Slattery1,
  6. Natalie Ryan1,
  7. Jonathan Schott1,
  8. Sebastian Crutch1
  1. 1Institute of Neurology
  2. 2Imperial College London

Abstract

Background and aims The clinico-neuroradiological syndrome posterior cortical atrophy (PCA) is the cardinal ‘visual dementia’. We evaluated oculomotor function in patients with PCA.

Methods 20 PCA patients, 17 typical Alzheimer's disease (tAD) patients and 22 healthy controls completed tests of fixation, saccade and smooth pursuit eye movements using an infrared pupil tracking system.

Results Eye movement abnormalities occur in 80% of PCA patients (compared to 17% tAD, 5% controls). PCA saccades were significantly hypometric, especially for distant targets. PCA patients were slower to reach saccadic targets whose onset overlapped with fixation, consistent with ‘sticky fixation’. Time to reach saccadic targets was also significantly associated with parietal and occipital cortical thickness measures. On fixation stability tasks, tAD patients showed more square wave jerks whose frequency was associated with lower cerebellar grey matter volume, whilst PCA patients showed characteristically large saccadic intrusions whose frequency correlated significantly with generalised reductions in cortical thickness. Smooth pursuit was also impaired, with lower gain in both PCA and tAD patient groups compared to controls.

Conclusions Eye movement abnormalities are near-ubiquitous in PCA, and may help distinguish PCA from tAD. We suggest the PCA oculomotor profile reflects weak input from degraded occipito-parietal spatial representations of stimulus location into a superior collicular spatial map for eye movement regulation. The results have implications for other patients with dementia-related visual impairment.

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